1. Field of the Invention
The present invention relates to an improved process for the preparation of aryl ethers and thioethers, and, more especially, to a process for the preparation of benzenoid ethers and thioethers by reacting an activated halobenzene with an anionic, organic oxygen-containing or sulfur-containing reactant.
By the term "activated halobenzene" as utilized herein, there is intended a halobenzene containing an electron-attracting group in the ortho- or para-position to the halogen, and by the term "anionic, organic oxygen-containing or sulfur-containing reactant" there is intended a reactant of the type RO.sup.- M.sup.+ or RS.sup.- M.sup.+, R being a hydrocarbon radical.
2. Description of the Prior Art
Known to the art is a process for the preparation of compounds of the general formula A--Y--A'--Z.sub.n, in which A and A' represent substituted or unsubstituted aryl radicals, Z is an electron-attracting group and Y is O, S or SO.sub.2, n being between 1 and 3. In accordance with this process, described in French Application No. 76/13,943 (U.S. Pat. No. 2,311,004), a compound of the formula A-YMe, in which Me represents an alkali metal or NH.sub.4, is reacted with a compound of the formula X--A--Z.sub.n, in which X is a halogen or an activated nitro group.
The reaction is carried out in a two-phase system, one of the phases being water or an alkaline aqueous medium, in which the compound A-YMe is reacted, and the other consisting of a solution of the compound X--A'--Z.sub.n in one or more water-immiscible solvents. The reaction is carried out in the presence of quaternary ammonium or phosphonium derivatives as catalysts.
The main disadvantages of this type of process are associated with the use of an aqueous phase. The presence of water mandates operation under pressure when the reaction temperature is above 100.degree. C. Furthermore, it involves the use of water-immiscible solvents which do not form emulsions with water in the presence of quaternary ammonium derivatives. Yet, some reactions only take place with appreciable yields when using aprotic polar solvents, such as sulfolane, dimethylsulfoxide and N-methylpyrrolidone, which are water-miscible solvents. It too will be appreciated that the large amount of water required, as is apparent from the examples in the abovementioned French patent application, makes it necessary to employ large reactors.
Further disadvantages result from the use of quaternary ammonium or phosphonium derivatives as catalysts. In fact, those skilled in the art are well aware that such catalysts easily degrade when exposed to temperatures above about 130.degree. C. Furthermore, serious difficulties are encountered, from an industrial point of view, in separating the catalyst from the reaction product.
An additional disadvantage of this type of prior art process lies in the fact that it does not permit the use of alcoholates which degrade in the presence of water.